Processing for iron-base alloy

ABSTRACT

An iron-base alloy of the nominal composition, by weight, of 15 percent chromium, 26 percent nickel, 1.3 percent molybdenum, 2.1 percent titanium, 0.3 percent vanadium, balance iron, is provided to provide a grain size of ASTM 5 or finer when measured at 1,000X magnification (normal ASTM grain size readings are at 100X magnification) with an ultimate tensile strength at room temperature of about 175,000 p.s.i.

United States Patent [191 Athey Jan.2,1973

[54] PROCESSING FOR IRON-BASE ALLOY [75] Inventor: Roy L. Athey, NorthPalm Beach,

Fla.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

[22] Filed: Aug. 5, 1971 [2]] Appl. No.: 169,534

[52] US. Cl. ..148/l2.3, 148/37, 148/38 [51] Int. Cl. ..C22c 39/20, C22c41/02, C21d 7/14 A [58] Field of Search ..l48/l2.3, 38, 37; 75/128 W,75/128 T, 128 B [56] References Cited UNITED STATES PATENTS 2,909,42610/1959 Richmond et al ..75/128 F 3,065,067 11/1962 Aggen ..75/128FPrimary Examiner-W. W. Stallard AttorneyRichard N. James [5 7 ABSTRACTAn iron-base alloy of the nominal composition, by weight, of 15 percentchromium, 26 percent nickel, 1.3 percent molybdenum, 2.1 percenttitanium, 0.3

percent vanadium, balance iron, is provided to provide a grain size ofASTM 5 or finer when measured at 1,000X magnification (normal ASTM grainsize readings are at lOOX magnification) with an ultimate tensilestrength at room temperature of about 175,000

p.s.i.

3 Claims, No Drawings PROCESSING FOR IRON-BASE ALLOY BACKGROUND OF THEINVENTION The present invention relates, in general, to the ironbasealloys and, more particularly, to novel processing therefor providing asignificant increase in mechanical properties.

Aerospace Materials Specification AMS 5525 C describes an alloy of thenominal composition, by weight, of percent chromium, 26 percent nickel,1.3 percent molybdenum, 2.1 percent titanium, 0.3 percent vanadium,balance substantially iron. As specified in AMS 5525 C, this alloy ascurrently processed has a maximum tensile strength of 105,000 p.s.i.after solutioning and a minimum tensile strength after full heattreatment of 140,000 p.s.i.

There is an urgent demand in certain applications for a structural alloyhaving a strength of about 180,000 p.s.i. These strength requirementsare satisfied by the nickel-base alloy specified in AMS 5597. However,for the particular application in mind, an iron-base alloy would bepreferred to a nickel-base alloy because of an anticipated exposure ofthe alloy to a high pressure hydrogen environment. In such anenvironment hydrogen embrittlement is much more severe in thenickel-base alloys than those having basis in iron. Thus, it isextremely important, if not essential, to have available an iron-basealloy whose physical properties approach that of the AMS 5597nickel-base alloy.

SUMMARY OF THE INVENTION The present invention provides an iron-basealloy having physical properties equivalent to the AMS 5597 nickel-basealloy, particularly a minimum tensile strength at room temperature, inthe fully heat treated condition, approaching 180,000 p.s.i.

The detailed specification chemistry for this alloy, as compared to theAMS 5525 C alloy is set forth in the following table:

TABLE I Composition (percent by weight) This invention AMS 5525 C Min.Max. Min. Max. Carbon 0.08 0.08 Manganese 0.10 2 Silicon 0.25 1Phosphorous 0.015 0.025 Sulfur 0.015 0.025 Chromium 13.5 16 13.5 16Nickel 24 27 24 27 Molybdenum 1 1.5 l 1.5 Titanium 1.9 2.3 1.9 2.3 Boron0.003 0.01 0.003 0.01 Vanadium 0.1 0.5 0.1 0.5 Aluminum 0.35 0.35 IronBalance Balance Rolling into sheet or strip conducted at a startingtemperature of about 1,800 F. with working down to about 1,550 F.produces a grain size too small to rate by ASTM charts at 100Xmagnification. Cold rolling with low temperature annealing may also beutilized to produce similar microstructures. Subsequent to the rollingoperation, processing is conducted at a temperature not exceeding1,550F., preferably in the range of 1350F.-1,450F. A low temperaturestabilization thus replaces the high temperature solution heattreatment. The alloy is then aged to provide maximum yield strength.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The conventional processing forthe AMS 5525 alloy is as follows:

1. rolling between 2,000F. down to 1,800F.;

2. solution heat treatment at 1,800F.;

3. and precipitation heat treatment at 1,325F. for 16 hours.

The processing according to the comparative embodiment of the presentinvention involves the following parameters and sequence:

1. rolling at 1,800F. down to 1,550F.;

2. stabilization at about 1,400F.;

3. and aging at about 1,300F. for 16 hours. (optional) The comparativeresults of the respective processing are summarized in the followingtables and compared, where appropriate, to the AMS 5597 nickel-basealloy goal:

TABLE 1] After step 1 Present AMS 5525 AMS 5597 Invention TensileStrength p.s.i., max. 120,000 105,000 140,000 Elongflw in 20 25 30 2 in.min. Rockwell Hardness (0.030 in.) B B90 TABLE III After step 3 PresentAMS 5525 AMS 5597 Invention Tensile Strength p.s.i., min. 175,000140,000 180,000 0.2% Strength 160,000 95,000 150,000 p.s.i., min.Elong.% in 2 in. min. 18 15 15 The following tables summarize the effectof the processing on a material of the appropriate chemistry.

TABLE IV Heat No. 8461 Rolled at 2,000F.

Subsequent H.T. Yield Ultimate F./hr./cool k.s.i. k.s.i. EL R/A 1800/l/0Q+ l300/l6/AC 98.4 158.2 27 44.7 (AMS 5525) 96.8 165.0 28 49.31700/l/OQ+ 100.8 168.3 28 47.1 1300/ 16/AC 1500/ I/OQ-l- 1300/16/AC137.1 176.2 22 31.3 AC 138.8 176.3 20 36.5

TABLE V Heat No. 8461 Rolled at 1,800F.

Subsequent H.T. Yield Ultimate F.lhr./cool k.s.i. k.s.i. EL R/A Thus, itwill be seen that the improved processing of the present inventionprovides an iron-base alloy having strength approaching that of the AMS5597'nickelbase alloy, as desired.

Although the invention has been specifically described in detail inconnection with specific examples and preferred embodiments, theinvention in its broader aspects is not limited thereto, but departuresmay be made therefrom within the scope of the accompanying claimswithout departure from the principles of the invention and withoutsacrificing its chief advantages.

What is claimed is:

1. Alloy sheet at a composition of about, by weight, 13-16 percentchromium, 24-27 percent nickel, l-2 percent molybdenum, 1.5-2.5 percenttitanium, 0.0030.0l percent boron, 0.1-0.5 percent vanadium, balancesubstantially iron, having at room temperature an ultimate tensilestrength in excess of about 170,000 p.s.i. and an 0.2 percent yieldstrength in excess of about 150,000 p.s.i.

2. Iron-base alloy sheet at a nominal composition, by weight, of about15 percent chromium, 26 percent nickel, 1.3 percent molybdenum, 2.1percent titanium and 0.3 percent vanadium, having at room temperature anultimate tensile strength of about 175,000 p.s.i. or higher and an 0.2percent yield strength of about 160,000 p.s.i. or higher.

3. The method of producing sheet from an alloy of the nominalcomposition of about, by weight, 15 percent chromium, 26 percent nickel,1.3 percent molybdenum, 2.1 percent titanium, 0.3 percent vanadium,balance substantially iron, which comprises:

rolling at a temperature not exceeding about and subsequently aging thealloy at a temperature of about 1,300F.,

the alloy after rolling being exposed to no sustained temperature inexcess of about 1 ,5 50F.

4 I1! l I i

2. Iron-base alloy sheet at a nominal composition, by weight, of about15 percent chromium, 26 percent nickel, 1.3 percent molybdenum, 2.1percent titanium and 0.3 percent vanadium, having at room temperature anultimate tensile strength of about 175,000 p.s.i. or higher and an 0.2percent yield strength of about 160, 000 p.s.i. or higher.
 3. The methodof producing sheet from an alloy of the nominal composition of about, byweight, 15 percent chromium, 26 percent nickel, 1.3 percent molybdenum,2.1 percent titanium, 0.3 percent vanadium, balance substantially iron,which comprises: rolling at a temperature not exceeding about 1,800* F.,and subsequently aging the alloy at a temperature of about 1, 300* F.,the alloy after rolling being exposed to no sustained temperature inexcess of about 1,550* F.